1. Field of Technology
This disclosure relates generally to ultrasonic inspection techniques and, more particularly, to apparatus and methods to perform subsea ultrasonic inspections.
2. Background Information
Ultrasound is a form of cyclical sound energy that travels as a waveform through a conducting medium (e.g., metal, liquid, body tissue, etc.). The frequency of an ultrasonic wave is above 20,000 Hz (or 20 KHz), generally greater than the upper threshold of human hearing.
The basic principles enabling ultrasonic technologies to be employed in inspection and diagnostic procedures are well-understood. Activating an ultrasonic probe (i.e. a device including a transmitter and a receiver of ultrasonic energy) positioned adjacent to the outer surface of an object of interest allows an image to be formed showing components internal to the object of interest. The ultrasonic wave is generated when an electric field is applied to one or more piezoelectric crystals located in the probe. Electrical stimulation causes mechanical distortion of the crystals causing them to vibrate and thereby produce sound waves (i.e. mechanical energy). An ultrasound image is generated when the pulsed sound waves emitted from the probe are transmitted into the object of interest, reflected off the interfaces of differing materials, and returned to the probe. The piezoelectric crystals of the probe, upon receiving the returning wave (i.e. echo), vibrate in response, and a transducer in the probe converts the mechanical energy from the vibrating crystals into an electrical signal, which is then processed and displayed as an image on a display screen.
A very common application of ultrasonic technologies is in the medical field where ultrasound enables a physician to visually observe the condition of a fetus, as well as tissue and other features internal to a patient's body. Due to its ability to image and display internal components of an object of interest, ultrasonic technologies have likewise been employed in the analysis and non-destructive testing of engineered structures, machines and other man-made products.
Subsea pipelines, products and structures associated with offshore oil and gas operations periodically require inspection and analysis. These objects may be located at the sea floor which, in some instances, may be 5,000-7,000 feet or more below the surface. At such depths, the water pressure exceeds 2,000 psi. Such depths and pressures may present difficult conditions in which to attempt ultrasonic inspection, and consequently, render some conventional equipment ineffective. For example, divers are unable to work at such depths, making the use of handheld ultrasonic probes impossible. Thus, carrying out ultrasonic inspection at such depths requires system components be carried to the sea floor and positioned by deep diving, remotely operated vehicles (ROV's) controlled by an operator at the surface. Not only may conventional ultrasonic technologies, systems and components be unable to withstand the subsea pressures encountered, but the components may be too fragile to be handled by the manipulating arms of the ROV. Further, accurately controlling the ROV from substantial distances, and using the ROV and its mechanical arms to position and operate components of conventional ultrasonic apparatus and systems, is impractical in many instances.
Accordingly, there remains a need in the art for improved devices and methods for employing ultrasonic inspection technologies subsea. Such devices and methods would be particularly well received if they offer the potential for use by subsea ROVs to ultrasonically inspect deepwater components.